Trace Metal and Nutrient Biogeochemistry

Trace metals like iron, cobalt, and zinc are essential vitamins for marine life. However, their scarcity limits biological growth in over one-third of the world's oceans. In seawater, these metals are tightly bound by organic molecules called ligands, which control whether they are available for organisms to use. Understanding the sources of these metals and how they are taken up by marine organisms is critical for predicting how ocean productivity will respond to human activities and climate change. Our research group has developed novel analytical techniques that address this long-standing critical knowledge gap by providing molecular level insight into the identity and distributions of organic ligands across the ocean. 

Most recently, we surveyed trace element speciation across the South Pacific and Southern Oceans as part of the US GEOTRACES GP17-OCE and GP17-ANT cruises. This study investigates the composition of trace element-binding ligands and their role in ocean biogeochemistry across contrasting regimes, known as low-productivity High Nutrient Low Chlorophyll (HNLC) regions and high biological productivity areas. Using liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) and inductively coupled plasma mass spectrometry (LC-ICPMS), we have characterized the chemical identity of natural ligands and siderophore biomarkers. We are also investigating the rates and mechanisms of photochemical reactions that degrade organic ligands and release metals. Our findings indicate the specific biological processes that control metal dissolution and transport in this critical marine environment and will aid modelling efforts that predict how productivity and carbon sequestration will change in the coming decades.

Despite accounting for approximately 5% of Earth’s land mass, wetland ecosystems store a staggering 20-30% of global terrestrial carbon. This makes wetlands a critical ecosystem for the carbon cycle. Our goal is to elucidate the biogeochemical cycles controlling carbon sequestration and flux from wetland systems. We do this by utilizing mass spectrometry techniques coupled to liquid chromatography to uncover reaction mechanisms that enhance organic matter stabilization, such as the formation of colloids and mineral associations under dynamic redox conditions. Our findings give insights for large data models that predict the potential for wetland systems to act as carbon sinks or emission sources in the face of changing environmental conditions. 

Nitrogen (N) is a limiting element in most of the surface ocean. Particularly, the primary productivity of phytoplankton is limited by the availability of dissolved organic nitrogen (DON). DON is the nitrogen-containing component of dissolved organic matter derived from the biosynthesis and decomposition of plants, algae, and microbes. There are various sources of DON contributing to the total DON pool in the ocean, such as river, submarine groundwater discharge, and N2 fixer Trichodesmium. Different sources of DON have distinct composition, bioavailability, and persistence. To differentiate DON from different inputs and track their fate, we use ultrahigh performance liquid chromatography with tandem Orbitrap mass spectrometry to characterize molecules, combined with computational algorithms (CoreMS) for data processing and analysis.